1. Field of the Invention
This invention relates to an improved method for the operation of a hydrodewaxing unit wherein a petroleum or shale oil fraction is contacted with a catalyst comprising a crystalline zeolite having a high silica/alumina mole ratio of at least 12 and a constraint index of from about 1 to about 12 under hydroprocessing conditions including a hydrogen atmosphere and elevated temperature and pressure. The improvement of the present method resides in increasing the average reactor temperature in a uniform manner to at least about 360.degree. C. within about the first seven days from start-up, said start-up being at an average reactor temperature of from about 200.degree. C. to about 310.degree. C.
2. Description of the Prior Art
Hydrocarbon conversion processes utilizing crystalline zeolite catalysts have been the subject of extensive investigation during recent years as is clear from both the patent and scientific literature. Crystalline alumino-silicates have been found to be particularly effective for a wide variety of hydrocarbon conversion processes and have been described and claimed in many patents including U.S. Pat. Nos. 3,140,249; 3,140,252; 3,140,251; 3,140,253; and 3,271,418. Aside from serving as general catalysts in hydrocarbon conversion processes, it is also known that the molecular sieve properties of zeolites can be utilized to preferentially convert one molecular species from a mixture of the same with other species.
In a process of this type a zeolite molecular sieve is employed having catalytic activity within its internal pore structure and pore openings such that one component of a feed is capable of entering within the internal pore structure thereof and being converted to the substantial exclusion of another component which, because of its size, is incapable of entering within the pores of the zeolitic material. Shape selective catalytic conversion is also known in the art and is disclosed and claimed in U.S. Pat. Nos. 3,140,322; 3,379,640 and 3,395,094.
Although a wide variety of zeolitic materials and particularly crystalline aluminosilicates have been successfully employed in various catalytic conversion processes, nevertheless, these prior art processes, in general, fell into one or two main categories. In one type of conversion process a zeolite was employed which had a pore size sufficiently large to admit the vast majority of components normally found in a charge, i.e., these materials are referred to as large pore size molecular sieves and they are generally stated to have a pore size of from 6 to 13 angstroms and are represented by zeolites X, Y and L. The other type of aluminosilicate was one which had a pore size of approximately 5 angstrom units and it was utilized to preferentially act upon normal paraffins to the substantial exclusion of other molecular species. Thus, by way of considerable over-simplification until recently, there were only two types of aluminosilicates which were available for hydrocarbon processing--those which would admit only normal paraffins and those which would admit all components normally present in a hydrocarbon feed charge. See U.S. Pat. No. 3,700,585 and Canadian Pat. No. 829,282.
The cracking and/or hydrocracking of petroleum stocks is in general well known and widely practiced. It is known to use various zeolites to catalyze cracking and/or hydrocracking processes.
Of particular recent interest has been the use of a novel class of catalysts to assist in the dewaxing of gas oils, lube base stocks, kerosines and whole crudes, including syn crudes obtained from shale, tar sands and coal hydrogenation. U.S. Pat. No. 3,700,585 discloses the use of ZSM-5 type zeolites to efficiently catalyze dewaxing of various petroleum feedstocks.
U.S. Pat. No. 3,700,585 discloses and claims the cracking and hydrocracking of paraffinic materials from various hydrocarbon feedstocks by contacting such feedstock with a ZSM-5 zeolite at about 290.degree. to 712.degree. C., 0.5 to 200 LHSV and with a hydrogen atmosphere in some cases. This patent is based upon work on the dewaxing of gas oils, particularly virgin gas oils, and crudes although its disclosure and claims are applicable to the dewaxing of any mixture of straight chain, slightly branched chain and other configuration hydrocarbons. The catalyst may have a hydrogenation/dehydrogenation component incorporated therein.
Other U.S. patents teaching dewaxing of various petroleum stocks are U.S. Pat. No. Re. 28,398; U.S. Pat. Nos. 3,852,189; 3,891,540; 3,894,933; 3,894,938; 3,894,939; 3,926,782; 3,956,102; 3,968,024; 3,980,550; 4,067,797 and 4,192,734.
Catalytic hydrodewaxing can be considered to be a relatively mild, shape selective cracking or hydrocracking process. It is shape selective because of the inherent constraints of the catalyst pore size upon the molecular configurations which are converted. It is mild because the conversions of gas oil feed to lower boiling range products are small, e.g. usually below about 35 percent and more usually below about 25 percent. It is operative over a wide temperature range but is usually carried out at relatively low temperatures, e.g. start of run temperatures of about 270.degree. C. are usual.